1. Technical Field
The present invention relates to a print position correcting device, a method of controlling the print position correcting apparatus, and a printing apparatus.
2. Related Art
In the past, there have been suggested various techniques for ejecting a liquid from a head unit onto exact positions on a print medium being transported in a printing apparatus such as an ink jet printer. For example, in an ink jet printer disclosed in JP-A-8-230194, ejection timing is corrected by detecting the transport speed of a print medium in order to land liquid droplets onto the exact positions on the print medium of which the transport speed is not uniform. In addition, in an ink jet printer disclosed in JP-A-2008-12712, the alignment of a line head is automatically adjusted with high precision to prevent a print defect such as an oblique line caused due to an alignment error of the line head.
In the ink printer disclosed in JP-A-8-230194, however, a change in the movement in a width direction of the print medium cannot be handled during printing. Moreover, when the print medium is obliquely transported in a transport direction or when the print medium is transported to a position deviated from the position to which the print medium was to be originally transported, such movement cannot be handled either. Accordingly, when the relative position of the head unit relative to the print medium is not uniform, an image cannot be formed in the intended region of the print medium. JP-A-2008-12712 discloses a method of aligning the line head of the ink jet printer. As in JP-A-8-230194, a change in the relative position of the head unit relative to the print medium cannot be handled during printing.